Complications in Spine Surgery: Expected Rates and Classification

Patient Perception of Complications

Preoperative expectations of risks and outcomes help determine whether patients perceive surgical procedures as successful. Preoperative counseling therefore plays an important role in establishing patient expectations and maximizing postoperative outcomes. Understanding comorbidity and risk factor associations with expected medical and surgical complication rates allows physicians to modify preoperative variables and appropriately counsel patients, to optimize postoperative outcomes. Additionally, understanding both patient and physician perceptions regarding the occurrence and severity of complications is crucial for counseling patients on expected outcomes and complication risks. Although surgeons and patients agree on the presence of complications, there is discordance on patient and surgeon perception of complication severity. For example, a cohort of 229 spine surgeons were surveyed and compared with 197 patients regarding the presence or absence of a complication in the context of 11 hypothetical scenarios. There was consistent agreement between surgeons and patients on presence of complications; however, notable variation arose between the cohorts when asked to rank the severity of complications, with patients consistently being more critical and ranking complications as more severe than surgeons. Similar findings were noted by Clavien et al. when using their classification system to correlate severity grades; they found significantly higher perceptions of surgical complication severity across all groups by patients as compared with physicians.

Despite the differences in patient and surgeon perceptions of complication severity, studies have also suggested that patients and surgeons can agree on complication severity when complications are properly classified. For example, agreement on complication severity was reached between patients and surgeons in roughly two-thirds (64%) of scenarios when complications were classified on a binary scale. After further assessment of the scenarios, definitions of major (severe medical complication or need for further surgery) and minor (transient events without permanent sequelae) complications were generated. Most notably, four of the scenarios featured purely medical adverse events, with no direct relation to the relevant surgery described. Both surgeons and patients definitively reported that a complication had occurred, which argues for the inclusion of medical adverse events within perioperative complications. Recently developed complication classification systems, such as the ISSG-AO Spine Complication Classification System ( Figs. 17.1 and 17.2 ), developed by the International Spine Study Group (ISSG), the AO Spine Deformity Knowledge Forum, and the European Spine Study Group (ESSG), are designed to account for both medical and surgical adverse events.

Complication Risk Factors

Optimization of modifiable risk factors is a key component in ensuring patient safety and maximizing postoperative outcomes in spine surgery. There are many risk factors for postoperative complications (see Box 17.1 ), including advanced age, tobacco use, obesity, and medical comorbidities such as cardiac and pulmonary disease, ^, as well as chronic preoperative opioid use. Male gender has also been cited as an independent risk factor for surgical morbidity. ^, Delving deeper into the relationship between advanced age and complications, inconsistent age thresholds used to define “elderly” has made comparison and generalization of results difficult. When spine patients were stratified by incrementally increasing 20-year age blocks, the Spinal Deformity Study Group found a significant increase in complications with each advancing age block. Similarly, a retrospective study performed by Daubs et al. of patients over the age of 60 years found that age over 69 years was associated with a sevenfold increase in complications. Despite increased risks of complications among elderly spine patients, studies have also demonstrated notable clinical improvement with operative management in the elderly population. This is further reflected by increased national rates of surgical intervention in elderly patients and decreased rates of postoperative complications among elderly patients, perhaps as a result of increased awareness and emphasis on preoperative optimization of complication risk factors. ^,

Similar to advanced age, obesity has been shown to negatively impact postoperative outcomes. ^, Burgstaller et al. demonstrated that patients with degenerative lumbar scoliosis benefit from surgical decompression; however, those with a body mass index (BMI) greater than 30 had a lower proportion of meaningful clinical benefit than those with a BMI less than 30. Increased BMI is significantly associated with postoperative complications and is an independent risk factor for infection. When Olsen et al. investigated risk factors for surgical site infection in 2008, obese patients were found to have a 2.2-fold increased risk of developing a surgical site infection.

Regarding medical complexity of patients, Whitemore et al. prospectively studied 226 patients undergoing spine surgery, and found that that increasing ASA grade was a significant risk factor for major complications and increased direct patient care costs. This was further corroborated by a retrospective review of nearly 23,000 patients from the Scoliosis Research Society Morbidity and Mortality database, reporting an overall complication rate of 8.4%, including 5.4% in ASA 1, 20.3% in ASA 2, and 50% in ASA 5 patients. These trends continued when separating medical and surgical complications, with ASA 4 correlating to 20% and 40% chances of surgical and medical complications, respectively.

In addition to preoperative optimization of medical comorbidities, intraoperative interventions may also help to minimize complication risks. For example, improper patient positioning with inadequate padding may cause peripheral nerve compression or skin breakdown. Therefore, optimal positioning via careful surgical frame selection and adequate modification of padding is paramount, especially in the obese patient population. Whether performing a revision adult spinal deformity (ASD) case or minimally invasive procedure, understanding the generalized risks associated with preoperative and intraoperative variables allows both modification of risks and proper adjustment of patient expectations.

Operative Complications

In a retrospective review of complications among 346 patients undergoing surgery for ASD, Smith et al. identified operative complications, specifically excessive blood loss and dural tears, as being among the most frequently encountered complications in ASD surgery. These intraoperative complications were independently associated with increased estimated blood loss (EBL) and greater LOS, but were not associated with worse patient outcomes, including health-related quality of life (HRQOL). ^, However, there was a significant increase in expense, with every extra hospital day adding $3000 to total costs. Additional complications unique to spine surgery and spinal deformity surgery ( Fig. 17.3 ) may significantly impact outcomes. Such complications include neurological dysfunction, with severity ranging from mild neuropraxia attributed to nerve root proximity during surgical approach, to severe complications such as inadvertent spinal cord injury. Neurological injury is not uncommon, with large series reporting neurological injury rates ranging from 17.6% to over 27% in adult deformity surgery. Regardless of surgical approach, performing an interbody fusion is an independent risk factor for intraoperative neurological injury, along with revision surgery and preexisting neurological deficit. ^{, ,} The majority of neurological injuries are first detected in the immediate postoperative period, highlighting the importance of the preoperative neurological examination because many of the postoperative deficits can be subtle.

Increased surgical invasiveness, such as combined anterior-posterior approach, three-column osteotomy, increased blood loss, increased number of operative levels, and increased surgical time, also increases risk of postoperative complications. In a retrospective case series including over 1000 patients, Farshad et al. found blood loss greater than 500 mL, increased operative time, and lumbosacral surgery were associated with perioperative morbidity. The impact of surgical invasiveness on complications is further reflected by rates of systemic coagulopathy reaching 53% with EBL greater than 3 L.